Pronounced in vitro and in vivo antiretroviral activity of 5-substituted 2,4-diamino-6-[2-(phosphonomethoxy)ethoxy] pyrimidines

OBJECTIVES

To discover new potent and selective anti-human immunodeficiency virus (HIV) acyclic nucleoside phosphonate (ANP) drugs with in vivo antiretroviral activity.

METHODS

New acyclic pyrimidine nucleoside phosphonate derivatives that mimic the structure of the anti-HIV purine nucleoside phosphonates 9-(2-phosphonylmethoxyethyl)adenine (PMEA, adefovir) and (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA, tenofovir) were designed by linking the acyclic side chain of the ANPs through an ether bond to the C-6 position instead of the N-1 position of the pyrimidine ring. The compounds were evaluated against HIV and Moloney murine sarcoma virus (MSV) in cell culture, including a broad variety of HIV-1 clade clinical isolates and relevant mutant (drug-resistant) HIV-1 isolates. Their antiviral activities were correlated and investigated in an in vivo model consisting of MSV-infected newborn mice. MSV-induced tumour formation and associated death were recorded in drug-treated animals.

RESULTS

Several 5-substituted 6-[2-(phosphonomethoxy)ethoxy]-2,4-diaminopyrimidine (PMEO-DAPy) analogues were found to inhibit a broad variety of HIV-1 clinical isolates. They showed a more favourable cross-resistance profile to mutant virus isolates than adefovir and tenofovir. There was a close correlation between inhibition of MSV in C3H/3T3 cells and inhibition of HIV-1 in CEM cells. The PMEO-DAPy derivatives potently inhibited MSV-induced tumour cell formation in newborn mice. The 5-methyl analogue PMEO-5-Me-DAPy proved markedly more inhibitory to MSV-induced tumour cell formation and associated animal death than its unsubstituted parent PMEO-DAPy derivative. When compared with adefovir, PMEO-5-Me-DAPy was less toxic and more antivirally active in MSV-infected mice.

CONCLUSIONS

PMEO-5-Me-DAPy deserves further (pre)clinical investigations as a candidate anti-HIV drug.

The scaffold protein Cybr is required for cytokine-modulated trafficking of leukocytes in vivo

Trafficking and cell adhesion are key properties of cells of the immune system. However, the molecular pathways that control these cellular behaviors are still poorly understood. Cybr is a scaffold protein highly expressed in the hematopoietic/immune system whose physiological role is still unknown. In vitro studies have shown it regulates LFA-1, a crucial molecule in lymphocyte attachment and migration. Cybr also binds cytohesin-1, a guanine nucleotide exchange factor for the ARF GTPases, which affects actin cytoskeleton remodeling during cell migration. Here we show that expression of Cybr in vivo is differentially modulated by type 1 cytokines during lymphocyte maturation. In mice, Cybr deficiency negatively affects leukocytes circulating in blood and lymphocytes present in the lymph nodes. Moreover, in a Th1-polarized mouse model, lymphocyte trafficking is impaired by loss of Cybr, and Cybr-deficient mice with aseptic peritonitis have fewer cells than controls present in the peritoneal cavity, as well as fewer leukocytes leaving the bloodstream. Mutant mice injected with Moloney murine sarcoma/leukemia virus develop significantly larger tumors than wild-type mice and have reduced lymph node enlargement, suggesting reduced cytotoxic T-lymphocyte migration. Taken together, these data support a role for Cybr in leukocyte trafficking, especially in response to proinflammatory cytokines in stress conditions.

Fluvastatin does not elevate periosteal osteogenesis induce by Moloney sarcoma virus (MSV) in mice

Several studies have demonstrated the pleiotropic effects of statins. Since Wang and associates reported that in rabbits lovastatin reduced steroid-induced bone loss, numerous authors have confirmed these data, however, others have reported conflicting results. In this study, the effects of fluvastatin on bone formation were investigated in early and late phase of osteogenesis. In the first set of experiments (early phase of osteogenesis) CFW/Ll mice were randomly divided into three groups. Two groups were injected with Moloney-murine sarcoma virus (Mo-MSV) into right thighs to induce orthotopic bone formation. Mice in the experimental group received fluvastatin for 11 consecutive days. Thirty days after Mo-MSV inoculation, total serum cholesterol, triglycerides, high- and low-density lipoprotein cholesterol, alkaline phosphatase (AP) were measured and bone mineral increase was calculated. In the second set of experiments (late phase of osteogenesis), fluvastatin was administered from day 11 after Mo-MSV inoculation for 20 consecutive days. Fluvastatin administration in the early phase of osteogenesis made no significant difference in average bone increase compared with mice receiving placebo. Lipid profile and AP were not significantly affected. During late phase of osteogenesis, the average increase in femural dry mass was significantly lower in the group of mice receiving fluvastatin than in the control group. Also, Mo-MSV-initiated tumors disappeared earlier in mice treated with fluvastatin. This may be attributed to the antioncogenic potential of fluvastatin. These results also point out that orthotopic bone formation at the sites of Mo-MSV inoculation in mice seems to be a useful model to examine the pleiotropic effects of statins.

The limitation of DEXA analysis for bone mass determination in mice

An increase in femoral and tibio/fibular bone mass following periosteal membrane stimulation by Moloney sarcoma virus inoculation into thigh muscles of mice was measured in situ on formalin fixed excised hind limbs using a Hologic 4500A Fan Beam X-ray bone densitometer adapted for small bone samples. These results were verified by measurements of constant dry bone mass of the same bones liberated from soft limb tissues by NaOH hydrolysis. There was no consistent data correlation found between the DEXA scan and dry bone mass evaluations. It is concluded that the sensitivity of the DEXA measurement is unsuitable when assessing very small bone samples, weighing merely 20-30 mg.

Na,K-ATPase beta-subunit is required for epithelial polarization, suppression of invasion, and cell motility

The cell adhesion molecule E-cadherin has been implicated in maintaining the polarized phenotype of epithelial cells and suppression of invasiveness and motility of carcinoma cells. Na,K-ATPase, consisting of an alpha- and beta-subunit, maintains the sodium gradient across the plasma membrane. A functional relationship between E-cadherin and Na,K-ATPase has not previously been described. We present evidence that the Na,K-ATPase plays a crucial role in E-cadherin-mediated development of epithelial polarity, and suppression of invasiveness and motility of carcinoma cells. Moloney sarcoma virus-transformed Madin-Darby canine kidney cells (MSV-MDCK) have highly reduced levels of E-cadherin and beta(1)-subunit of Na,K-ATPase. Forced expression of E-cadherin in MSV-MDCK cells did not reestablish epithelial polarity or inhibit the invasiveness and motility of these cells. In contrast, expression of E-cadherin and Na,K-ATPase beta(1)-subunit induced epithelial polarization, including the formation of tight junctions and desmosomes, abolished invasiveness, and reduced cell motility in MSV-MDCK cells. Our results suggest that E-cadherin-mediated cell-cell adhesion requires the Na,K-ATPase beta-subunit's function to induce epithelial polarization and suppress invasiveness and motility of carcinoma cells. Involvement of the beta(1)-subunit of Na,K-ATPase in the polarized phenotype of epithelial cells reveals a novel link between the structural organization and vectorial ion transport function of epithelial cells.

Production and characterization of a bicistronic Moloney-based retroviral vector expressing human interleukin 2 and herpes simplex virus thymidine kinase for gene therapy of cancer

Gene-based therapeutic strategies for cancer mainly include augmentation of immunotherapeutic and chemotherapeutic approaches. In this study we report the design and functional assay of a novel bicistronic Moloney-based retroviral vector expressing human interleukin-2 (IL-2) and herpesvirus thymidine kinase (tk) through a cap-dependent translation and an internal ribosome entry site (IRES)-regulated translation, respectively. This construct has the potential for allowing combination of cytokine and suicide gene therapy, especially in areas such as the brain, composed of post-mitotic cells refractory to transduction by type C retroviral vectors. Accordingly, human glioma cells were used as targets for gene transfer after selecting a packaging cell clone that produced a reasonable titer of recombinant virus and expressed high levels of IL-2 and tk transcripts. Although transduction efficiency was reduced in glioma cells as compared with murine NIH 3T3 cells, transgene expression was effectively achieved. Transduced glioma cells were sensitive to ganciclovir and secreted around 1000 U/ml IL-2 in the culture supernatants. Simultaneous production of IL-2 and tk in vivo by genetically treated tumor cells would hopefully potentiate the effect of gangiclovir-induced metabolic suicide, possibly by boosting the immune response associated with tumor debulking or by amplifying the bystander response.

Increased beta-actin expression in an invasive moloney sarcoma virus-transformed MDCK cell variant concentrates to the tips of multiple pseudopodia

An invasive variant of Moloney sarcoma virus-transformed MDCK cells (MSV-MDCK-INV), which was isolated by the repeated selection of cells that successfully traversed a Matrigel-coated filter, exhibits increased motile ability and presents an elongated cell shape and numerous pseudopodia. Although stress fibers are present in both MDCK and MSV-MDCK cells, MSV-MDCK-INV cells contain no stress fibers and exhibit a dense concentration of actin at the tips of pseudopodia. Relative to both MDCK and MSV-MDCK cells, the MSV-MDCK-INV cells exhibit increased expression of beta-actin and redistribution of beta-actin to the tips of pseudopodia. These actin concentrations are enriched in both F- and G-actin and, thus, represent dynamic regions of actin cytoskeleton remodeling. The acquisition of invasive properties by epithelial transformants is, therefore, associated with the increased expression of beta-actin and its concentration in actin-rich domains, which may drive pseudopodial extension and facilitate tumor cell invasion.

Effects of amphetamine on the development of Moloney sarcoma virus-induced tumors in mice

Experiments were conducted to evaluate the effects of amphetamine (0. 4 mg/kg) on the development of autochthonous tumors induced by the Moloney sarcoma virus (MSV) in Balb/c female mice. Enhancement of MSV-induced tumor incidence and tumor growth was observed, together with a delay in the usual prompt regression of the tumors, when mice were daily injected with amphetamine for 3 days after MSV-inoculation. However, no effects of amphetamine on tumor development were observed when it was administered during the 3 days before tumor inoculation.

AMF-R tubules concentrate in a pericentriolar microtubule domain after MSV transformation of epithelial MDCK cells

Autocrine motility factor receptor (AMF-R) is localized to an intracellular microtubule-associated membranous organelle, the AMF-R tubule. In well-spread untransformed MDCK epithelial cells, the microtubules originate from a broad perinuclear region and AMF-R tubules extend throughout the cytoplasm of the cells. In Moloney sarcoma virus (mos)-transformed MDCK (MSV-MDCK) cells, microtubules accumulate around the centrosome, forming a microtubule domain rich in stabilized detyrosinated microtubules. AMF-R tubules are quantitatively associated with this pericentriolar microtubule domain and the rough endoplasmic reticulum and lysosomes also co-distribute with the pericentriolar mass of microtubules. The Golgi apparatus is closely associated with the microtubule organizing center (MTOC) within the juxtanuclear mass of AMF-R tubules, and no co-localization of AMF-R tubules with the Golgi marker beta-COP could be detected by confocal microscopy. After nocodazole treatment and washout, microtubule nucleation occurs exclusively at the centrosome of MSV-MDCK cells, and only after microtubule extension to the cell periphery does the microtubule cytoskeleton reorganize to generate the pericentriolar microtubule domain after 30-60 min. AMF-R tubules dispersed by nocodazole treatment concentrate in the pericentriolar region in parallel with the reorganization of the microtubule cytoskeleton. MSV transformation of epithelial MDCK cells results in the stabilization of a pericentriolar microtubule domain responsible for the concentration and polarized distribution of AMF-R tubules.

CD28 is not required for rejection of unmanipulated syngeneic and autologous tumors

To gain a better understanding of the requirement of CD28 co-stimulation in different types of T cell-dependent tumor rejection responses, we performed a series of syngeneic and autologous tumor rejection experiments on CD28 knockout mice. In a preimmunization-challenge model, virally-induced ALC lymphoma and methylcholanthrene-induced MC57X fibrosarcoma transplants were rejected similarly by syngeneic CD28 knockout and immunocompetent controls. ALC-specific cytotoxic T lymphocytes (CTL) and MC57X-specific tumor necrosis factor (TNF) release were induced in CD28 knockouts, although at a reduced level in the latter case. Secondly, the spontaneous regression of Moloney murine sarcoma virus (MMSV)-induced primary tumors in the autologous hosts occurred equally in CD28 knockouts and in immunocompetent control mice. A comparable virus-specific CTL response was generated in both, as revealed in cytolytic assays against RBL-5 targets. Thirdly, the spontaneous rejection of the B7-transfected EL-4 lymphoma by immunocompetent hosts was abrogated in CD28 knockout mice, since more than 82% CD28 knockouts developed tumors after inoculation with B7-transfected EL-4 cells. Our results therefore show that CD28 co-stimulatory molecules are not required for the rejection of unmanipulated syngeneic tumors in hyperimmunized hosts and the regression of MMSV-induced sarcoma in autochthonous hosts.

A novel, transformation-relevant activation domain in Fos proteins

We have previously demonstrated that transformation by Fos is critically dependent on an intact DNA-binding domain (bZip) and a functional N-terminal transactivation motif (N-TM). We now show that a novel motif (C-terminal transactivation motif [C-TM]) near the C terminus also plays an important role in both transformation and the activation of AP1-dependent transcription and that the hydrophobic amino acids in the C-TM are functionally essential. The C-TM is the most crucial element in the C-terminal transactivation domain in Fos, as indicated by its relative strength and context-independent function. The C-TM is clearly different from the previously identified HOB2 domain, located N terminally to the C-TM, and the C-terminally positioned TATA-binding protein-binding domain. We also show that the C-terminal transactivation domain strongly synergizes with the HOB1-like N-TM, even when both domains are present on different proteins within a dimeric complex, and that the C-TM plays a crucial role in this cooperation. These observations can be corroborated in a model in which multiple contacts with the basal machinery are established either to stabilize the transcription complex or to facilitate its sequential assembly.

Anti-L-selectin monoclonal antibody treatment in mice enhances tumor growth by preventing CTL sensitization in peripheral lymph nodes draining the tumor area

To examine the in vivo contribution of L-selectin in the sensitization of tumor-specific CTL, we investigated the effects of treatment with the anti-L-selectin monoclonal antibody (MAb) MEL-14 on the immune response to Moloney-murine sarcoma virus (M-MSV)-induced tumors, which exhibit spontaneous regression following generation of a strong virus-specific CTL response. Daily systemic administration of MEL-14 for 10 days to M-MSV-injected mice gave rise to larger sarcomas that persisted for a longer time, compared with those arising in control mice injected with virus only. The enhanced tumor growth could not be attributed to cytotoxic activity on leukocytes by MEL-14 since no reduction in the total cell number was detected in peripheral blood and spleen of MAb-treated mice. Evaluation of the immunological response in MAb-treated animals revealed a strong reduction in the generation of virus-specific CTL precursors (CTLp) in tumor-draining peripheral lymph nodes (PLN) 10 and 15 days after M-MSV injection, while in spleen, where lymphocyte localization is independent of L-selectin expression, CTLp generation was only delayed. By day 20, when tumors had begun to regress, the CTLp number showed a marked increase in both spleen and local PLN, where naive recirculating CTL could now enter because L-selectin was no longer down-regulated or blocked by the injected MAb. Our findings indicate that functional inactivation of L-selectin by MEL-14 treatment prevented migration of naive L-selectin+CTL through high endothelial venules (HEV) and their accumulation in PLN draining the tumor area, thereby precluding the initiation of a tumor-specific CTL response that takes place primarily at this site.

Inverse relation of autocrine motility factor receptor and E-cadherin expression following MDCK epithelial cell transformation

Autocrine motility factor interacts with its cell surface receptor (AMF-R) to stimulate tumor cell motility. To study AMF-R expression following transformation of polarized epithelial MDCK cells, we have used the invasive Moloney sarcoma virus transformed MDCK (MSV-MDCK) cell population. Decreased E-cadherin expression of the transformed MSV-MDCK clones is associated with both increased cellular motility and increased AMF-R expression. Increased AMF-R expression is due to MSV transformation as differentially motile MSV-MDCK clones, which either retain low E-cadherin, exhibit equivalent high levels of AMF-R. Loss of the polarized epithelial phenotype and increased cellular motility following transformation of MDCK cells is thus associated with a shift from a high E-cadherin/low AMF-R to a low E-cadherin/low AMF-R phenotype.

Role of anti-LFA-1 and anti-ICAM-1 combined MAb treatment in the rejection of tumors induced by Moloney murine sarcoma virus (M-MSV)

We investigated the effect of combined treatment with anti-LFA-1 and anti-ICAM-1 monoclonal antibodies (MAbs) in the immune reaction to Moloney-murine-sarcoma-virus(M-MSV)-induced tumors, which spontaneously regress due to the generation of a strong virus-specific cytotoxic-T-lymphocyte(CTL) response. Repeated systemic administration of both MAbs to M-MSV-injected mice enhanced tumor growth and delayed regression, while treatment with a single MAb had a similar, though less pronounced, effect. The immune depression achieved could not be attributed to lymphocyte depletion, because no reduction in the total number of leukocytes was detected in the peripheral blood or spleen of these mice. However, anti-LFA-I MAb, alone or in combination with anti-ICAM-I MAb, prevented lymphocyte homing in tumor-draining lymph nodes. Cytofluorimetric analysis disclosed a profound down-modulation of LFA-I and ICAM-I molecule expression on T cells following in vivo MAb treatment. Moreover, in anti-LFA-I MAb-treated mice, the receptor was coated to saturation, while anti-ICAM-I MAb treatment brought about ICAM-I-molecule-coating levels below saturation. Evaluation of M-MSV-specific CTL precursor (p) frequency in lymphoid organs of mice receiving combined MAb treatment showed that CTL generation was greatly reduced 10 days after M-MSV injection, and returned to control levels by day 15. Our findings indicate that systemic administration of MAbs to LFA-I and ICAM-I molecules brings about a strong immune suppressive effect which is mainly due to a block in T-lymphocyte re-circulation, and activation by tumor cells. However, this immune-depressive effect is only temporary, and strictly dependent on continuous MAb administration. Thus, our data suggest that treatment with anti-LFA-I and anti-ICAM-I MAbs combined is unable to induce T-cell tolerance in a highly immunogenic system.

A temporal study of the lesions induced by MoMuSV-349

We used time point studies to document the progression of neoplasms, haematologic abnormalities and associated lesions induced by Moloney murine sarcoma virus-349 (MoMuSV-349). BALB/c mice inoculated intraperitoneally with MoMuSV-349 first developed histologically discernible lesions at 14 days post-inoculation (d.p.i.). The initial neoplasms were characterized by whorls of fusiform or spindle-shaped cells enmeshing dense infiltrates of neutrophils and macrophages. By 21 d.p.i., clinical signs associated with MoMuSV-349 infection were evident. The distribution of the neoplasms was more widespread, although the histologic appearance of the tumours was very similar to that found at 14 d.p.i. All mice sacrificed at 28 d.p.i. exhibited characteristic clinical signs associated with MoMuSV-349, including moderate cachexia. Histologically, neoplasms observed at 28 d.p.i. contained a significant vascular component. By 35 d.p.i., all mice exhibited severe clinical signs (e.g. cachexia, dull hair coat, uneven gait). Histologically, all the neoplasms had a predominant vascular component. Non-neoplastic lesions, such as severe thymic atrophy and multifocal pulmonary haemorrhage, were commonly present. Mice sacrificed 42 d.p.i. were clinically, grossly and histologically similar to those sacrificed at 35 d.p.i. However, one difference found in the 42 d.p.i. group was the presence of rare rhabdomyosarcomas infiltrating the skeletal muscles. Mice inoculated with MoMuSV-349 developed severe neutrophilia and lymphopenia, and moderate anaemia. This study demonstrates that MoMuSV-349 induced angiosarcomatous neoplasms are characterized by stage development and severe haematologic and non-neoplastic abnormalities.

Efficacy of oral 9-(2-phosphonylmethoxyethyl)-2,6-diaminopurine (PMEDAP) in the treatment of retrovirus and cytomegalovirus infections in mice

9-(2-Phosphonylmethoxyethyl)-2,6-diaminopurine (PMEDAP) is a broad-spectrum antiviral agent with potent activity against DNA viruses and retroviruses. We now demonstrate that PMEDAP is highly efficacious when given orally to mice infected with either Moloney murine sarcoma virus (MSV), Friend leukemia virus (FLV), or murine cytomegalovirus (MCMV). PMEDAP markedly delayed MSV-induced tumor initiation when administered orally at 50, 100, or 250 mg/kg/day during 5 subsequent days. At the highest dose (250 mg/kg/day), PMEDAP completely prevented tumor formation in the MSV-infected animals. PMEDAP also caused 84-96% inhibition of FLV-induced splenomegaly when given orally to FLV-infected mice at 50-250 mg/kg/day. These PMEDAP treatment regimens were also markedly effective in increasing the survival rate of MCMV-infected mice. Intraperitoneal PMEDAP achieved a comparable antiviral activity at 2- to 5-fold lower doses than oral PMEDAP. However, the therapeutic index (ratio of the toxic dose to the antivirally effective dose) of oral PMEDAP was substantially higher than that of intraperitoneal PMEDAP. Oral PMEDAP at doses of 100, 250, or 500 mg/kg resulted in plasma PMEDAP levels of 0.5-2.5 micrograms/ml, which were sustained for 3 or 6 hours after administration and may account for the high antiviral efficacy achieved.

In vitro differentiation of rhabdomyosarcomas induced by nickel or by Moloney murine sarcoma virus

In vitro cultures and clonal derivatives have been established from rat rhabdomyosarcomas induced by Moloney-Murine Sarcoma Virus (MSV) or by nickel sulfide; differentiation ability has been studied as expression of desmin, embryonic and adult myosin isoforms, alpha-actin isoforms and cellular fusion. The two rhabdomyosarcoma models showed different levels of myogenic differentiation. Multinucleated myotube-like structures were frequently observed in cultures derived from nickel-induced tumours. Desmin was present in 50-80% of cells and embryonic myosin in up to 10%. In MSV-tumour-derived cultures and in their metastases or clonal derivatives two cell types are present in different ratios: spindle-shaped cells, adherent to plastic surfaces, and rounded cells, loosely attached or floating free in the medium. These cultures showed features of myogenic differentiation (10-80% desmin-positive cells), but embryonic myosin expression and production of multinucleated myotube-like structures were very rare events. Cultures from autochthonous lymph node and lung metastatic cells showed similar patterns of differentiation. Retinoic acid increased differentiated features (myotube formation and embryonic myosin expression) only in nickel-induced rhabdomyosarcoma cells. The two models described here mimic the heterogeneity in differentiation pattern found among human rhabdomyosarcomas. Myogenic differentiation ability was retained at a good level by nickel-induced tumours, whereas it was strongly impaired in MSV-induced tumours.

Inhibitory effects of 9-(2-phosphonylmethoxyethyl)adenine and 3'-azido-2',3'-dideoxythymidine on tumor development in mice inoculated intracerebrally with Moloney murine sarcoma virus

9-(2-Phosphonylmethoxyethyl)adenine (PMEA), a potent inhibitor of human immunodeficiency virus (HIV), caused a dose-dependent suppression of tumor formation, and mortality associated therewith, in 6-day-old NMRI mice inoculated intracerebrally with Moloney murine sarcoma virus (MSV). Even at a dose as low as 1 mg/kg/day, PMEA effected a significant delay in tumor formation. When evaluated in parallel with PMEA, 3'-azido-2',3'-dideoxythymidine (AZT) conferred a comparable tumor-inhibitory effect at a 5- to 10-fold higher dose than PMEA. Prolonged treatment of MSV-infected mice with PMEA resulted in long-term survivors without apparent signs of tumor development. In view of the propensity of HIV to spread to the central nervous system (CNS), the marked activity shown by PMEA against experimental retrovirus infection of the brain in mice points to its potential in the treatment of AIDS and other retrovirus infections of the CNS.

In vitro induction of early mouse embryo intracisternal particles (epsilon particles) in cultured cell lines

The experimental induction of epsilon particles, retrovirus-like structures corresponding to the small IA particles of the mouse, was studied by electron microscopy in rodent-cultured cell lines. Among the chemicals tested, only IdUr was shown to be an effective inducer, but not cycloheximide, puromycin , deoxy-fluorouracil or 5-azacytidine. However, only two mouse-derived cell lines: Ki-BALB and FG 10, among 27 cell lines of mouse, rat and mink origins tested, expressed epsilon particles upon IdUr treatment. Epsilon particles thus respond to chemical inducers very differently in comparison with large IAP. Moreover, the addition of interferon previously shown to attenuate IAP production, had no effect on that of epsilon particles.

Interferon-induced inhibition of Moloney sarcoma virus-transformed cells: requirement for T-cells

We previously demonstrated that although natural killer (NK) cells participated in interferon (IFN)-induced inhibition of growth of the Moloney sarcoma MSC cell tumor, the need for NK cells could be circumvented by using a small tumor cell challenge or an increased amount of IFN. These studies were performed in normal, euthymic mice. The role of T-cells remained undefined. In the present study, nude mice were used to evaluate the role of T-cells. Investigation of various treatment regimens revealed that IFN could not totally inhibit tumor growth in nude mice. A significant delay in tumor growth was observed when 1 x 10(5) units of IFN were administered at the site of tumor on days 1-4 after tumor challenge. Increasing the dose of IFN or extending therapy to 7 days did not afford any further inhibition of tumor growth. In vivo depletion of NK cells with anti-asialo monoganglioside antibody revealed that the delay in tumor growth was dependent on NK cells when IFN was given on days 1-4. Treatment for days 1-7, however, still inhibited tumor growth in the NK cell-depleted nude mice. In order to further ascertain the role of T-cells in IFN-induced tumor inhibition, T-cell reconstitution studies of nude mice were performed. Nude mice were reconstituted with 1 x 10(7), 2 x 10(7), and 5 x 10(7) T-cells on day -1 to tumor challenge and treated with IFN on days 1-7. The extent of the observed decrease of tumor sizes and tumor incidences among the T-cell-reconstituted groups was dependent on the dose of T-cells being administered in both IFN-treated and untreated animals. These data indicate that T-cells are essential for maintaining the growth-inhibitory effects of IFN. This is in contrast to NK cells whose role in IFN-induced inhibition of MSC tumor growth can be circumvented by increasing the dose of IFN.

Inhibition of Moloney murine lymphoma and sarcoma growth in vivo by dietary retinoids

The effects of dietary retinoids on the growth of Moloney lymphoma (LSTRA) and sarcoma (MSC) in BALB/c mice were evaluated. Transplantable syngeneic Moloney lymphoma and sarcoma tumors are immunogenic. Preimmunization with LSTRA cells provides protection against subsequent challenge and sarcomas spontaneously regress following injection of an appropriate inoculum of MSC cells. In normal mice fed varying concentrations of all-trans-retinoic acid (RA) and given injections of 10(3) LSTRA cells, RA caused a dose-dependent increase in the number of survivors; 50% of the mice fed RA at 50 mg/kg of diet were long-term survivors. All animals died that were fed a control diet and challenged with 10(3) LSTRA cells. Athymic (nu/nu) mice fed RA were not protected against lymphoma growth, whereas euthymic (nu/+) mice were; therefore, the antitumor effect of RA was thymus dependent. Primary immunization with irradiated LSTRA in the presence of RA caused a significant increase in cell-mediated cytotoxicity by spleen cells at 4 days after immunization. However, challenge of animals preimmunized with LSTRA in the presence of dietary RA revealed a dose-dependent inhibition of memory. A significant reduction in MSC growth was also observed in normal mice fed 13-cis-retinoic acid (cRA). A comparison of the primary antilymphoma effect of dietary RA, cRA, N-(all-trans-retinoyl)-DL-leucine (RL), and N-(4-hydroxyphenyl)retinamide (4-HPR) revealed an efficacy hierarchy of RL greater than RA greater than cRA greater than 4-HPR with RL producing 70% long-term survivors at 115 days after challenge with 10(3) LSTRA cells. These studies indicate that retinoids can inhibit the growth of transplantable, retroviral-induced, immunogenic tumors by thymus-dependent mechanisms and that a newly synthesized retinoylamino acid (RL) is more potent than RA at inhibiting Moloney lymphoma growth.

Effect of recombinant human interleukin 2 on the growth of a BALB/c sarcoma induced by Moloney murine sarcoma virus

The effect of in vivo administration of recombinant interleukin 2 (rIL2) on the growth of a primary female BALB/c sarcoma induced by Moloney murine sarcoma virus (M-MSV) was studied. Although low-dose administration of (6,000 JU/mouse x 14 days) rIL2 had no effect on the growth of the tumors, high-dose (15,000-80,000 JU/mouse x 14 days) intraperitoneal inoculation of rIL2 induced tumor regression, dose-dependently. Tumors in mice which received 80,000 JU/mouse/day of rIL2 regressed completely 2 weeks after the initiation of treatment. The survival rates of the treated groups were significantly higher than those of the control group. A time course experiment disclosed that the effect of rIL2 was restricted only to the group in which rIL2 treatment started 8 days after the inoculation of M-MSV. The cytotoxic activity of regional lymph node lymphocytes from rIL2-treated mice was demonstrated against primary culture of M-MSV-induced sarcoma but not against syngeneic tumor induced by methylcholanthrene (Meth A). The effect of rIL2 was partially blocked by the administration of anti-IL2 receptor antibody. Immunohistochemical examination revealed that infiltration of Thy1.2+Lyt1+2- (helper/inducer subset) lymphocytes into the tumor tissue was prominent in mice which received high-dose rIL2. The results indicated that IL2 induced regression of M-MSV-induced sarcoma mainly through activation of IL2-receptor-positive helper T cells in the tumor tissues and of killer cells in the draining lymph nodes.

Histopathologic studies on myeloproliferative sarcoma virus (MPSV) induced leukemias and hemangiosarcoma in Jar-2 rats

It is well known that MPSV induces myeloproliferative syndrome (MPS) in mice. Intravenous one shot inoculation of myeloproliferative sarcoma virus (MPSV) with Friend murine leukemia virus (F-MuLV) as a helper in newborn Jar-2 rats (on the second neonatal day) yielded hematopoietic malignancies in all the treated rats (25/25 rats) after 2 weeks' latency. MPS appeared from the 14th day in 14 rats. In the midst of the myeloproliferative field of the spleen and bone marrow, myeloblastic or myeloblastic-erythroblastic foci were observed. From 19th day, acute myeloblastic leukemia occurred in 3 rats and erythroleukemia in 8 rats. MPSV induced first MPS which remained as such or later developed into acute leukemia. Myelofibrosis as seen in mice was not observed. In addition, hemangiosarcoma of the brain, spinal cord and spleen appeared in 15 rats from the 24th day, and were often multiple. MPSV can yield the tumor only in newborn rats, and target cells of MPSV are not only hematopoietic cells but also endothelial cells of the brain, spinal cord and occasionally spleen.

Experimental rat model for human yolk sac tumor

The morphological and biological characteristics of experimentally induced rat yolk sac carcinomas (ysca) are compared to those of human yolk sac tumors. It is shown that the rat ysca shares many morphological and biological properties with its human counterpart although the cellular origin is probably different. Whereas the human yolk sac tumors are believed to be of germ cell origin, the rat visceral yolk sac-derived tumors are not. The hypothesis is formulated that the rat ysca are derived from multipotential cells different from germ cells, and which originate in the extra-embryonic membrane after displacement.

Uptake of cadmium-109, a metallothionein-binding radiometal, by tumors in mice as a function of the transformed phenotype

Metallothionein (MT) is an intracellular protein that binds many metals with isotopes having imaging or radiotherapeutic potential. To determine whether uptake of radioisotopes that bind to MT is increased in tumors, we measured the uptake of cadmium-109 (Cd-109) in tumors and in normal tissues of mice. Tumors were grown in Balb/C mice from cultured Balb/3T3 cells transformed by the Moloney murine sarcoma virus (MMSV). Uptake of Cd-109 by MMSV tumors exceeded that by normal tissues examined, with the exception of liver and kidney (the organs known to be richest in metallothionein). The MMSV tumor:background ratios of activity were greater for Cd-109 than for gallium-67 for many of the normal tissues examined. The magnitude of uptake of Cd-109 by tumors from four related cell lines paralleled their degree of expression of two indices of the transformed, or malignant, phenotype. We conclude that metals that bind to MT may be useful for imaging or radiotherapy of cancer.

Defects in lens fiber differentiation are linked to c-mos overexpression in transgenic mice

We describe three strains of transgenic mice derived by embryo microinjection of DNA consisting of a long terminal repeat (LTR) of Moloney murine sarcoma virus (Mo-MSV) linked to the murine c-mos coding sequences. Southern analysis of the genomic DNA of these strains suggested that in each case the transgene had integrated at a different chromosomal location. The strains were characterized by dominant changes in secondary lens fiber differentiation. Shortly after birth, insufficient elongation of differentiating lens fibers and lack of basement membrane secretion resulted in breakdown of the posterior lens capsule. This, in turn led to posterior protrusion and swelling of lens tissue. In the course of the first 3 weeks after birth, globular lens cells began to fill the entire anterior and posterior chambers of the eye. Concomitantly, there was massive overexpression of c-mos RNA in the lens. Whereas this construct has high transforming activity when transfected into NIH-3T3 cells, no hyperplasia or neoplasia have been observed in the affected lenses. Increased expression of c-mos RNA was not confined to the lens of the eye but has been detected in any of several tissues tested.

Rat transformation-associated proteins (TAP) induced by Moloney murine sarcoma virus interact with specific receptors on normal rat kidney cells

In this report, data are presented to show that transformation-associated proteins (TAP) secreted from the transformed 6M2 cells have mitogenic activities in the stimulation of DNA synthesis and proliferation of normal rat kidney (NRK-2) cells and of nonpermissively grown 6M2 cells. TAP also bound specifically to NRK-2 cells with a binding dissociation constant (Kd) of 1.4 pM. Approximately 2 X 10(5) binding sites per cell were found. Therefore, TAP may represent a set of virally-induced growth stimulatory factors.

Myosin isoform expression in rat rhabdomyosarcoma induced by Moloney murine sarcoma virus

Myosin isoform expression was analyzed in experimental rhabdomyosarcoma (RMS) using monoclonal antibodies (mAbs) and immunofluorescence techniques. Tumors induced by inoculating newborn rats with Moloney murine sarcoma virus (Mo-MSV) were examined 30-90 days after birth. Nine tumors and two lymph node metastases were studied by direct, indirect, and double immunofluorescence assays using a panel of five anti-myosin mAbs. The mAb BF-45 was specifically reactive with embryonic myosin heavy chain (MHC), mAb BF-34 was specific for a neonatal MHC epitope, mAb BF-B6 was directed against an epitope present in both embryonic and neonatal MHC, and mAbs BF-F3 and BF-32 detected epitopes present in adult MHC isoforms. Anti-desmin antibodies were also used for comparison. The results of this study show that: (1) the majority of neoplastic cells stained for desmin while only a minority of neoplastic cells were labeled by anti-myosin antibodies; (2) myosin positive tumor cells contained predominantly embryonic and neonatal MHC types but rare RMS cells reacted exclusively with anti-adult myosin antibodies; and (3) adult and embryonic MHC phenotypes were occasionally detected within the same tumor cell especially in RMS with the longest latencies. Together these results would suggest that the mechanism(s) regulating MHC gene expression in skeletal muscle cells can be altered by the transforming activity of Mo-MSV.

Lactate dehydrogenase-elevating virus induces anti-Golgi apparatus antibodies

A recently described autoantibody-inducing agent in mice was further characterized. Tentatively designated AGIA (anti-Golgi apparatus-inducing agent), this agent has previously been shown to cause antibody production against Golgi apparatus (GA) antigen of cells from different vertebrate species as well as against tumour surface antigen of the Moloney murine sarcoma virus-non-producer transformant Sac. It was shown to possess the properties characteristic of lactate dehydrogenase-elevating virus (LDV). It induced elevation of lactate dehydrogenase levels in the blood, persistent lifelong viraemia in mice and serum titres of up to 10(11) infectious doses (ID50) per ml in the acute phase of infection. Its replication in vitro was limited to subpopulations of murine peritoneal macrophages. Electron microscopy of AGIA-infected macrophages and of serum of infected mice revealed virus-like particles with a morphology resembling LDV. The buoyant density of AGIA was approximately 1.14 g/ml. Both the enzyme-elevating activity and the autoantibody-inducing activity were shown to belong to LDV. Infection of STU mice with two established strains of LDV (LDVROW and LDVPLA) was also found to induce both autoantibody groups. In both cases, after infection with AGIA as well as after infection with the two known LDV isolates, anti-Sac cell antibodies occurred at comparable titres. However, anti-GA antibody titres were rather low after infection with LDVROW and LDVPLA compared with AGIA infection. Serological cross-reactivity was demonstrated between AGIA-, LDVROW- and LDVPLA-infected macrophages. AGIA induced anti-GA antibodies in all six mouse strains tested (STU, DBA/2, BALB/c, C3H/He, NMRI, C57BL/6); however, anti-Sac cell antibodies did not develop in C57BL/6 mice.

T-cell immunity to murine Moloney sarcoma virus-induced tumours: L3T4+ T cells are necessary for resistance to primary sarcoma growth, but Lyt-2+ T cells are required for resistance to secondary tumour cell challenge

Experimental protocols have been devised to deliniate the importance of T-cell subsets in immunity to Moloney sarcoma virus-induced tumours using the surface antigens L3T4 and Lyt-2 as markers of helper and cytotoxic cells, respectively. Because the monoclonal antibodies used have been shown to deplete T-cell subsets in vivo, we have been able to study the role of L3T4+ and Lyt-2+ T cells in the primary response to MSV for the first time. The results clearly show that L3T4+ T cells are the most important in resistance to the viral challenge. Mice injected with monoclonal antibodies to L3T4 grew large tumours following injection of a viral innoculum that was resisted by untreated mice or mice injected with monoclonal antibodies to Lyt-2. The same monoclonal antibodies were used to remove primed L3T4+ or Lyt-2+ T cells in vitro in adoptive transfer experiments. Normal unirradiated mice were protected from a challenge of WR19L lymphoma cells when they were given primed spleen and lymph node cells intraperitoneally. Depletion of Lyt-2+ T cells before adoptive transfer abolished this protective effect. Depletion of L3T4+ cells had no effect on the ability of primed cells to transfer immunity. Thus, while L3T4+ T cells are required for the primary rejection of MSV, only primed Lyt-2+ T cells are able to transfer resistance to a secondary challenge of lymphoma cells.

Monoclonal IgM antibodies that inhibit primary Moloney murine sarcoma growth

Monoclonal IgM antibodies with specificity for Moloney murine sarcoma virus (M-MuSV)-Moloney murine leukemia virus (M-MuLV) from two hybridoma clones have been isolated and characterized. The monoclonal antibodies have specificity for a cytoplasmic and cell surface Friend-Moloney-Rauscher group-specific antigen. Immunoelectron microscopy revealed antibody binding to the surface of virus-expressing cells but not to the budding virus particles. Treatment of M-MuSV-injected mice with monoclonal IgM anti-M-MuSV significantly inhibited tumor growth compared to virus-inoculated animals receiving either saline or MOPC 104E. Nude mice exhibited delayed tumor induction following treatment with the monoclonal antibodies but ultimately died from tumor growth. Virus-injected euthymic mice that were treated with monoclonal IgM anti-M-MuSV generated a potentiated spleen cell-mediated cytotoxicity against Moloney sarcoma cells compared to virus-infected treated with saline. This potentiation of cytotoxicity remained after trypsinization of the spleen cells and thus was probably not due to passively adsorbed monoclonal antibody. The antibodies alone or in the presence of complement did not neutralize M-MuLV. The IgM antibodies induced specific tumor cell cytotoxicity in vitro mediated by complement spleen cells, lymph node cells, or thymus cells. In conclusion, two monoclonal IgM anti-M-MuSV antibodies that bind to the tumor cell surface did not neutralize virus can inhibit primary M-MuSV-induced tumor growth in vivo. The regression event appeared to involve heterogeneous mechanisms. Complete regression remained thymus dependent even with passive antibody therapy, but significant tumor growth inhibition was produced independent of T-cells. In vitro these IgM antibodies induced complement and cell-mediated cytotoxicity.

Prostaglandin E2 content of regressing and progressing Moloney sarcomas

Regressing mouse Moloney sarcomas contain macrophages that are activated for tumor cell killing, while those found in progressively growing sarcomas either cannot kill or do so very poorly. Prostaglandin E2 (PGE2) has been shown to down-regulate macrophage activation in vitro. The study described here was designed, therefore, to ascertain and compare the concentrations of PGE2 in regressing and progressing Moloney sarcomas. Tumors were harvested for extraction and analyzed using conditions that minimized artifactual increases in PGE2 levels attributable to de novo synthesis. Concentrations of PGE2 were higher in progressing, compared to regressing, Moloney sarcomas during the early stages of tumor development. At nearly all time points, however, whether the neoplasms were of regressing or progressing type, the estimated concentrations of PGE2 in tumors exceeded the level that completely inhibits macrophage activation for tumor cell killing in vitro, that is, 10(-8) M. These data suggest either that PGE2 is not responsible for down-regulating activation in Moloney sarcomas or that, if PGE2 is responsible for the negative regulation of activation in progressing Moloney sarcomas, there must be something in regressing sarcomas that prevents the hormone from having its inhibitory effect.

Differential induction of H-2K vs H-2D class I major histocompatibility complex antigen expression by murine recombinant interferon-gamma

The results presented here indicate that recombinant murine interferon-gamma can cause a dramatic differential induction of two distinct class I MHC molecules. Thus, IFN-gamma treatment of the murine leukemia virus (MuLV)-induced AKR SL3 tumor, a cell line that normally expresses moderate levels of class I MHC antigens, resulted in a large increase in H-2Dk expression, but no change or a slight decrease in H-2Kk expression as measured by cytofluorography. Explanations of the selective enhancement of Dk expression based on increased Fc receptor display or differential kinetics of induction were ruled out. The phenomenon was observed over a wide range of doses of IFN-gamma and with two different monoclonal antibodies to Kk, the latter finding making it unlikely that an altered form of the Kk molecule was induced. The same differential induction of the Dk antigen was observed for the LBRM.5A4 tumor cell line. Because LBRM.5A4 is also MuLV+ but of congenic B10.BR (H-2k) origin, these results were consistent with the possibility that such differential induction was associated with the H-2k haplotype and/or MuLV. The implications of these results, as a possible mechanism of tumor cell escape from an immune surveillance system monitored by class I MHC-restricted T cells and as a useful model system to dissect the mechanism of IFN-gamma induction of class I MHC antigens, are discussed.

Ectopic hematopoiesis in peritoneal tumor nodules induced by the myeloproliferative sarcoma virus in DBA/2 mice

Tumor nodules composed of fibroblasts, large undifferentiated cells, granulocytes, and small lymphocytes develop in the spleens of adult DBA/2 mice infected with the myeloproliferative sarcoma virus (MPSV). They spread thereafter in the organism, and at the terminal stage of the disease they are especially numerous on the peritoneal membrane. The present study, performed on those tumor nodules to avoid contamination by exogenous hematopoietic cells, demonstrated that they were sites of granulopoiesis, which may have occurred via the local differentiation of granulomacrophage precursor cells (GM-CFC) and perhaps also from pluripotent hematopoietic stem cells, since these two populations were present in the tumor nodules (25 +/- 11 and 13 +/- 10, respectively, per 5-10(5) cells). Almost all (88%) those GM-CFC were able to clone in vitro without added colony-stimulating factor. A comparative study with the Moloney murine sarcoma virus-induced tumor indicated that the local production of hematopoiesis-stimulating factors was not sufficient to allow such ectopic granulopoiesis. These results imply the presence of a specific hematopoietic microenvironment in the MPSV-induced tumor nodules.

Opposing effects of the interferon inducer, avridine: enhancement or suppression of tumor growth depending on treatment regimen

Tumor growth and regression was studied in C57BL/6J mice injected with Moloney sarcoma virus (MSV) and treated with the interferon (IFN)-inducing drug, avridine. Avridine decreased the persistence of tumors when given one or five days after virus, but shortened the prepatent period and increased persistence if given one day prior to virus. Additional studies were undertaken to study the role that serum interferon and natural killer (NK) cell activity might have in this phenomenon. Interferon levels were greatly enhanced (over that induced by virus alone or avridine alone) when avridine was given one day after, but not one day before, virus. Six days after viral infection, interferon titers had returned to near zero but could be boosted by injecting avridine at day 5. Multiple injections of avridine before and after virus resulted in refractoriness to interferon induction and tumor persistence. NK activity was greatly increased by virus at two days post-infection, and avridine given one day after infection significantly enhanced cytotoxicity of these splenic cells against tumor cells. By six days after infection, NK activity had returned to normal but could be increased by avridine given at five days post-infection. It appeared that high levels of interferon induced by avridine given at one or five days after infection increased NK activity and may have been responsible for enhanced regression. Pre-treatment by avridine had little effect on interferon levels over that induced by virus alone, but that did not explain the enhancement of tumor growth since NK activity was increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Stage-dependent induction of prenatal tumors in mice by the Kirsten and Moloney strains of murine sarcoma viruses

The Moloney (MoMSV) and Kirsten (KiMSV) strains of murine sarcoma viruses are known to induce mesenchymal sarcomas upon infection of newborn rodents. To determine their activity in mouse embryos, 11- to 15-day-pregnant CD-1 mice were laparotomized, and the single implants were inoculated into the abdominal portion of the embryonal body with an average of 15 and 1500 focus-forming particles/g of body weight of the MoMSV and KiMSV viruses, respectively. Another group of less than 1-day-old pups was given a comparable amount of either virus. Tumors appeared in the young within the first few weeks of life with incidences and histological types dependent on the gestational day and the viral strain inoculated. Mixed mesenchymal sarcomas at or near the site of inoculation and vascular tumors of the brain were by far the most frequent neoplasms observed in the newborn. With MoMSV there was an increased incidence of sarcomas with advancing age at treatment, being 0% at 11 days of pregnancy and 96% in newborn (P for trend, less than 0.025). By contrast, KiMSV caused an incidence of sarcomas below 20% throughout (P for trend, greater than 0.05). Brain tumors were identified in the several MoMSV and KiMSV groups, with a peak value of 43% following the inoculation of both viruses into 13- and 15-day-old embryos, respectively. While the total incidence of these tumors was significantly different from controls, no positive trend by day of treatment was found among the MoMSV and KiMSV viruses (P less than 0.05). The tumors were mainly capillary angiomas, but a few cavernous angiomas were also detected. In addition, eight pups which were given injections of both viruses at developmental Days 11 to 13 had tumors of the choroid plexus. In many instances, newborn pups were affected by multiple vascular abnormalities of the brain, including capillary telangiectases and multiple hemorrhagic areas. No such lesions nor tumors at any site were found among the control animals. The present results are important not only because of the evidence that Swiss embryos respond selectively to the carcinogenic effects by murine sarcoma viruses, but also because they offer the opportunity to dissect directly in vivo the mechanisms underlying the stage-related sensitivity of prenatal mice to oncogenic retroviruses.

Orthotopic and ectopic chondrogenesis and osteogenesis mediated by neoplastic cells

In mice, tumors of various origins have been found to stimulate cambium layer cells of periosteum/ perichondrium of adjacent orthotopic bone or cartilage to proliferate and/or differentiate into osteoblasts or chondroblasts. Tumors may induce new bone and/or cartilage formation. In progressively growing tumors the osteogenic/chondrogenic activity is gradually surpassed by the resorptive processes mediated either by osteoclasts, directly by tumor cells, or by tumor stroma. In regressing tumors, however, the deposits of new bone remained unresorbed, resulting in a permanent gain of bone mass. In human subjects, similar changes were observed in bone adjacent to carcinoma development. Stimulation of periosteal bone formation was observed at earlier stages of the disease, while bone resorption mainly by tumor cells and their stroma was observed in later stages of tumor development. The unresponsiveness of the heterotopically-induced bone to the Moloney sarcoma virus, in contrast to the response of orthotopic bone clearly indicates that ectopic bones do not develop a true periosteum.

T-cell regulation of erythropoiesis during acute lymphoblastic leukemia

How and where erythropoiesis is maintained during advanced leukemic disease is an important and, as yet, unresolved question in hematology. To address the potential role of T-lymphocytes as cells that regulate CFU-E differentiation during leukemogenesis, an experimental model of disease has been developed in inbred Balb/c mice. Specifically, three-week-old Balb/c By mice were injected with murine sarcoma virus-murine leukemia virus-Moloney (MSV-MuLV-M), which resulted 6-8 months later in the development of immunoblastic T-cell sarcomas with a leukemic phase. Splenic T cells from either normal or tumor-bearing mice were assessed for their relative ability to modulate erythroid differentiation. Quantitatively, T cells, Ly1 or Ly 2,3 T-cell subsets isolated from tumor-bearing animals significantly enhanced erythropoiesis when compared with comparable normal T-cell subsets. These data suggest that the compensatory shift of erythropoiesis from the bone marrow to the spleen observed during leukemogenesis was facilitated by splenic T cells. In this circumstance, the enhanced erythropoietic function may be mediated by splenic T cells, which are selectively activated by virus.

Influence of Toxoplasma on manifestations of Moloney virus infections

Considerable evidence documents the importance of co-factors, including the immune response, in expression of oncogenicity of tumour viruses. To determine whether a common protozoal infection that can depress lymphocyte function alters manifestations of oncogenic virus infection, a mouse model of Toxoplasma infection with depressed T lymphocyte function was developed. In this model, Toxoplasma depressed blastogenic transformation to the T-cell mitogen Concanavalin A and primary antibody response to sheep red blood cells which requires T cell help. Uninfected and Toxoplasma-infected mice were then infected with Moloney leukaemia or Moloney sarcoma viruses and development of lymphoma and sarcoma were evaluated. Toxoplasma infection, which induced depression of T-cell function, decreased the incidence of Moloney sarcoma virus induced rhabdomyosarcomas but did not alter progression or regression of tumour in those mice that developed tumour. Conjoint infection with Toxoplasma and Moloney leukaemia virus did not increase incidence of lymphoma when compared with incidence of lymphoma in mice infected with Moloney leukaemia virus alone.

Increased secretion of type beta transforming growth factor accompanies viral transformation of cells

Cells transformed by Harvey or Moloney sarcoma virus secrete at least 40 times as much type beta transforming growth factor as their respective untransformed control cells. The transformed cells bind only 20 to 50% as much type beta transforming growth factor as the control cells, suggesting that transformation causes down-regulation of the type beta transforming growth factor receptor.

Procoagulant activity of macrophages associated with different murine neoplasms

Mononuclear phagocytes, an integral part of the lymphoreticular infiltrate of human and experimental tumors, might contribute to tumor-associated fibrin deposition through the development of procoagulant activity (PCA). We have investigated PCA of tumor-associated macrophages (TAM) in 6 transplanted murine tumors in syngeneic hosts; peritoneal macrophages from tumor-bearing and control animals were studied also, as reference cell populations. PCA was evaluated by a one-stage clotting assay immediately after preparation and following incubation in the absence and in the presence of endotoxin. TAM from 5 poorly immunogenic tumors (mFS6, MN/MCA1, R 80/44, M109 and MS2) had basal PCA levels comparable to or somewhat lower than those of peritoneal macrophages from the same animals. Similar PCA was found in peritoneal macrophages from both control and tumor-bearing animals. Unlike peritoneal macrophages, TAM in all instances failed to respond with increased PCA when exposed to endotoxin in vitro. Failure to respond to endotoxin could not be ascribed to contaminating tumor cells or their products, to the presence of suppressive macrophage populations or to the lack of lymphocyte "help". TAM from a strongly immunogenic, regressing tumor (MSV sarcoma), in contrast to its non-immunogenic variant, MS2, and to the 4 other tumors mentioned above, expressed high levels of PCA immediately after isolation. The latter did not increase further following in vitro stimulation with endotoxin. When MSV sarcomas were induced in nude mice, TAM showed PCA levels similar to those of the euthymic hosts, suggesting that the procoagulant response was largely independent of T-cell-mediated immunity.

Infection and transformation of dog cells with a modified sarcoma virus

Dog-embryo cell cultures were infected with a mixture of feline leukemia virus (FelLV) and a modified murine (Moloney) sarcoma virus MSV(FelLV). Morphological alteration of the cells was observed 3 days post infection. Virus progeny from the infected cultures increased 50- to 100-fold in foci of cellular alteration on dog cell cultures pretreated with diethylaminoethyl-dextran, but only twofold on cat embryo cultures similarly treated. The numbers of foci produced corresponded to a dual infection with the MSV(FelLV) and endogenous FelLV and could be increased by simultaneous infection with exogenous FelLV. After five serial passages in dog cell cultures, the virus mixture still had a superior focus-inducing capacity on cat cells as compared with dog cells. Electron microscopic examination of infected dog cultures showed typical C-type virions. FelLV alone propagated in dog cell cultures without inducing morphological alteration, and progeny virus, capable of promoting focus formation by MSV(FelLV), could be detected 48 hours post infection.